I know the feeling! But it actually is likely an inflammation of the levator scapulae not traps... I sometimes get the same... at one point I had to put Voltaren (anti-inflammatory cream) on the side of my head!!!
I find that I get this more when I do lifts from the hang or when I lower the weight down instead of dropping the weight on the floor between reps... it is the action of dropping the weight than suddenly catching it between reps that causes it.
Are you doing the lifts from the hang?